The invention relates in general to fine liquid mist fire protection/suppression systems for fire extinguishment. In particular, the invention relates to an effervescent fine liquid mist-type system that uses chemical reactions to produce a bubbly two-phase flow output through a nozzle or array of nozzles.
Fluorocarbon-based fire extinguishants are environmentally harmful because they cause depletion of the earth's ozone layer. Present U.S. law and treaty requires the phase out and replacement of such materials under the 1988 Montreal Protocol, which classified Halon as a Class I Ozone Depleting Substance (ODS), and which called for limits on global production by over 100 developed nation signatories. Furthermore, the U.S. Clean Air Act Amendments of 1990 call for the ban on production of Halon in the U.S after January 1994. This law also prohibits purposeful venting and requires training personnel involved with their use to minimize their emission into the atmosphere. The U.S. Navy has responded to the requirements of these acts by prospectively prohibiting the use of ODSs and by finding and using alternative designs in fire extinguishment systems. Therefore, a need exists to replace all halon systems and improve existing water sprinkler based systems for more effective fire extinguishment use.
Fine liquid mist type systems have very favorable characteristics as a replacement for existing Halon systems. Typically, such systems include nozzles for creating misting fluids using a pressurized gas and such type systems are well-known. A liquid is injected into a central bore of a nozzle that directs a high-velocity gas. In some nozzles, the velocity and pressure of the gas are increased in a narrowed throat area of the bore, which causes atomization of the fluid into small droplets as the gas travels through the nozzle. To aid atomization and provide an unobstructed flow path for the gas, the fluid is usually injected into the gas stream through an aperture in the bore wall so that the two different fluid streams impinge at a 90-degree angle. Nozzles of the above-described type require high-pressure spraying of the liquid and the gas, which is undesirable. Another problem with these mixing nozzles is that the liquid and gas must be sprayed through fine holes of a small diameter, which can easily clog or wear away.
The use of water as a spray for fire extinguishment is well-known. Liquid-only, water spray nozzles for fire extinguishment create water droplets by deflecting the water flow just ahead of the spouting aperture. The droplet's size is relatively large and a desirable fine water mist cannot be achieved. The need for a low-pressure, reliable, liquid/gas mixing nozzle which is effective for fire extinguishment is disclosed in U.S. Pat. No. 5,520,331 issued on May 28, 1996 to Joseph E. Wolfe and entitled "Liquid Atomizing Nozzle", which patent is hereby expressly incorporated by reference. In the '331 patent, the nozzle structure effects an extremely fine, liquid atomization with low pressurization of the liquid and gas that are delivered to the nozzle. Furthermore, the fluid and gas are delivered through relatively large apertures so that wear and clogging are minimized. The '331 patent also discloses a convergent/divergent (C-D) gas nozzle affixed to a mixing block having a liquid delivery tube with an aperture that is centered within a gas conduit and located just upstream of a narrowed throat of the nozzle.